U.S. patent application number 12/116905 was filed with the patent office on 2008-11-13 for epoxidation catalyst, a process for preparing the catalyst, and a process for the production of an olefin oxide, a 1,2-diol, a 1,2-diol ether, a 1,2-carbonate, or an alkanolamine.
Invention is credited to Marek Matusz.
Application Number | 20080281118 12/116905 |
Document ID | / |
Family ID | 39865078 |
Filed Date | 2008-11-13 |
United States Patent
Application |
20080281118 |
Kind Code |
A1 |
Matusz; Marek |
November 13, 2008 |
EPOXIDATION CATALYST, A PROCESS FOR PREPARING THE CATALYST, AND A
PROCESS FOR THE PRODUCTION OF AN OLEFIN OXIDE, A 1,2-DIOL, A
1,2-DIOL ETHER, A 1,2-CARBONATE, OR AN ALKANOLAMINE
Abstract
A catalyst for the epoxidation of an olefin comprising a carrier
and, deposited on the carrier, silver, a rhenium promoter, a first
co-promoter, and a second co-promoter; wherein the quantity of the
rhenium promoter deposited on the carrier is greater than 1
mmole/kg, relative to the weight of the catalyst; the first
co-promoter is selected from sulfur, phosphorus, boron, and
mixtures thereof; the second co-promoter is selected from tungsten,
molybdenum, chromium, and mixtures thereof; and the total quantity
of the first co-promoter and the second co-promoter deposited on
the carrier is at most 3.8 mmole/kg, relative to the weight of the
catalyst; a process for preparing the catalyst; a process for
preparing an olefin oxide by reacting a feed comprising an olefin
and oxygen in the presence of the catalyst; and a process for
preparing a 1,2-diol, a 1,2-diol ether, a 1,2-carbonate, or an
alkanolamine.
Inventors: |
Matusz; Marek; (Houston,
TX) |
Correspondence
Address: |
SHELL OIL COMPANY
P O BOX 2463
HOUSTON
TX
772522463
US
|
Family ID: |
39865078 |
Appl. No.: |
12/116905 |
Filed: |
May 7, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60916947 |
May 9, 2007 |
|
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Current U.S.
Class: |
558/260 ;
502/200; 502/204; 502/206; 502/209; 502/210; 502/211; 502/220;
502/221; 564/503; 568/679; 568/680 |
Current CPC
Class: |
B01J 23/688 20130101;
B01J 23/002 20130101; B01J 2523/00 20130101; Y02P 20/142 20151101;
C07C 68/04 20130101; B01J 27/055 20130101; C07C 213/04 20130101;
Y02P 20/141 20151101; C07C 29/106 20130101; C07D 301/10 20130101;
B01J 27/188 20130101; B01J 2523/00 20130101; B01J 2523/18 20130101;
B01J 2523/30 20130101; B01J 2523/60 20130101; B01J 2523/74
20130101; B01J 2523/00 20130101; B01J 2523/11 20130101; B01J
2523/15 20130101; B01J 2523/18 20130101; B01J 2523/62 20130101;
B01J 2523/69 20130101; B01J 2523/74 20130101; B01J 2523/00
20130101; B01J 2523/11 20130101; B01J 2523/15 20130101; B01J
2523/18 20130101; B01J 2523/62 20130101; B01J 2523/68 20130101;
B01J 2523/74 20130101; C07C 68/04 20130101; C07C 69/96 20130101;
C07C 29/106 20130101; C07C 31/20 20130101 |
Class at
Publication: |
558/260 ;
502/210; 502/211; 502/221; 502/220; 502/204; 502/206; 502/200;
502/209; 564/503; 568/679; 568/680 |
International
Class: |
B01J 27/188 20060101
B01J027/188; B01J 27/047 20060101 B01J027/047; B01J 27/051 20060101
B01J027/051; B01J 27/24 20060101 B01J027/24; C07C 41/01 20060101
C07C041/01; B01J 27/19 20060101 B01J027/19; B01J 27/186 20060101
B01J027/186 |
Claims
1. A catalyst for the epoxidation of an olefin comprising a carrier
and, deposited on the carrier, silver, a rhenium promoter, a first
co-promoter, and a second co-promoter; wherein the quantity of the
rhenium promoter deposited on the carrier is greater than 1
mmole/kg, relative to the weight of the catalyst; the first
co-promoter is selected from the group consisting of sulfur,
phosphorus, boron, and mixtures thereof; the second co-promoter is
selected from the group consisting of tungsten, molybdenum,
chromium, and mixtures thereof; and the total quantity of the first
co-promoter and the second co-promoter deposited on the carrier is
at most 3.8 mmole/kg, relative to the weight of the catalyst.
2. The catalyst as claimed in claim 1, wherein the quantity of the
rhenium promoter is at least 1.5 mmole/kg, relative to the weight
of the catalyst.
3. The catalyst as claimed in claim 1, wherein the total quantity
of the first co-promoter and the second co-promoter is at most 3.5
mmole/kg, relative to the weight of the catalyst.
4. The catalyst as claimed in claim 1, wherein the total quantity
of the first co-promoter and the second co-promoter is at least 0.5
mmole/kg, relative to the weight of the catalyst.
5. The catalyst as claimed in claim 1, wherein the second
co-promoter comprises tungsten.
6. The catalyst as claimed in claim 1, wherein the second
co-promoter comprises molybdenum.
7. The catalyst as claimed in claim 1, wherein the first
co-promoter comprises sulfur.
8. The catalyst as claimed in claim 1, wherein the catalyst further
comprises a further element selected from the group consisting of
nitrogen, fluorine, alkali metals, alkaline earth metals, titanium,
hafnium, zirconium, vanadium, thallium, thorium, tantalum, niobium,
gallium and germanium and mixtures thereof.
9. The catalyst as claimed in claim 8, wherein the alkali metals
are selected from the group consisting of lithium, sodium, and
cesium.
10. The catalyst as claimed in claim 1, wherein the catalyst
further comprises deposited on the carrier a potassium promoter in
a quantity of at least 0.5 mmole/kg, relative to the weight of the
catalyst.
12. The catalyst as claimed in claim 1, wherein the catalyst
further comprises deposited on the carrier a potassium promoter in
a quantity of at least 1.5 mmole/kg, relative to the weight of the
catalyst.
13. The catalyst as claimed in claim 1, wherein the catalyst has a
water extractable quantity of potassium in the range of from 1.25
to 10 mmole/kg, relative to the weight of the catalyst.
14. The catalyst as claimed in claim 1, wherein the catalyst has a
water extractable quantity of potassium in the range of from 1.5 to
7.5 mmole/kg, relative to the weight of the catalyst.
15. The catalyst as claimed in claim 1, wherein silver is present
in a quantity in the range of 10 to 500 g/kg, relative to the
weight of the catalyst.
16. The catalyst as claimed in claim 1, wherein silver is present
in a quantity in the range of 50 to 450 g/kg, relative to the
weight of the catalyst.
17. A process for preparing a catalyst for the epoxidation of an
olefin comprising depositing silver, a rhenium promoter, a first
co-promoter, and a second co-promoter on a carrier; wherein the
quantity of the rhenium promoter deposited on the carrier is
greater than 1 mmole/kg, relative to the weight of the catalyst;
the first co-promoter is selected from the group consisting of
sulfur, phosphorus, boron, and mixtures thereof; the second
co-promoter is selected from the group consisting of tungsten,
molybdenum, chromium, and mixtures thereof; and the total quantity
of the first co-promoter and the second co-promoter deposited on
the carrier is at most 3.8 mmole/kg, relative to the weight of the
catalyst.
18. The process as claimed in claim 17, wherein the second
co-promoter comprises tungsten.
19. The process as claimed in claim 17, wherein the second
co-promoter comprises molybdenum.
20. The process as claimed in claim 17, wherein the first
co-promoter comprises sulfur.
21. The process as claimed in claim 17, wherein the rhenium
promoter is deposited in a quantity in the range of from 1.25 to 50
mmole/kg, relative to the weight of the catalyst.
22. The process as claimed in claim 17, wherein the process further
comprises depositing on the carrier a further element selected from
the group consisting of nitrogen, fluorine, alkali metals, alkaline
earth metals, titanium, hafnium, zirconium, vanadium, thallium,
thorium, tantalum, niobium, gallium and germanium and mixtures
thereof.
23. The process as claimed in claim 17, wherein the process further
comprises depositing on the carrier a potassium promoter in a
quantity of at least 0.5 mmole/kg, relative to the weight of the
catalyst.
24. A process for preparing an olefin oxide by reacting a feed
comprising an olefin and oxygen in the presence of a catalyst as
claimed in claim 1.
25. The process as claimed in claim 24, wherein the olefin
comprises ethylene.
26. A process for preparing a 1,2-diol, a 1,2-diol ether, a
1,2-carbonate, or an alkanolamine comprising converting an olefin
oxide into the 1,2-diol, the 1,2-diol ether, the 1,2-carbonate, or
the alkanolamine, wherein the olefin oxide has been prepared by the
process for preparing an olefin oxide as claimed in claim 24.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 60/916,947, filed May 9, 2007, which is
incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to an epoxidation catalyst, a
process for preparing the catalyst, and a process for the
production of an olefin oxide, a 1,2-diol, a 1,2-diol ether, a
1,2-carbonate, or an alkanolamine.
BACKGROUND OF THE INVENTION
[0003] In olefin epoxidation, a feed containing an olefin and
oxygen is contacted with a catalyst under epoxidation conditions.
The olefin is reacted with oxygen to form an olefin oxide. A
product mix results that contains olefin oxide and, typically,
unreacted feed and combustion products.
[0004] The olefin oxide may be reacted with water to form a
1,2-diol, with carbon dioxide to form a 1,2-carbonate, with an
alcohol to form a 1,2-diol ether, or with an amine to form an
alkanolamine. Thus, 1,2-diols, 1,2-carbonates, 1,2-diol ethers, and
alkanolamines may be produced in a multi-step process initially
comprising olefin epoxidation and then the conversion of the formed
olefin oxide with water, carbon dioxide, an alcohol, or an
amine.
[0005] Olefin epoxidation catalysts typically comprise a silver
component, usually with one or more additional elements deposited
therewith, on a carrier. U.S. Pat. No. 4,766,105 discloses an
ethylene oxide catalyst comprising silver, alkali metal, rhenium
and a rhenium co-promoter selected from sulfur, molybdenum,
tungsten, chromium and mixtures thereof supported on a carrier. The
ethylene oxide catalyst described in U.S. Pat. No. 4,766,105
provides an improvement in one or more catalytic properties.
[0006] The catalyst performance may be assessed on the basis of
selectivity, activity and stability of operation. The selectivity
is the fraction of the converted olefin yielding the desired olefin
oxide. As the catalyst ages, the fraction of the olefin converted
normally decreases with time and to maintain a constant level of
olefin oxide production the temperature of the reaction may be
increased.
[0007] The selectivity determines to a large extent the economical
attractiveness of an epoxidation process. For example, one percent
improvement in the selectivity of the epoxidation process can
substantially reduce the yearly operating costs of a large scale
ethylene oxide plant. Further, the longer the activity and
selectivity can be maintained at acceptable values, the longer the
catalyst charge can be kept in the reactor and the more product is
obtained. Quite modest improvements in the selectivity, activity,
and maintenance of the selectivity and activity over long periods
yield substantial dividends in terms of process efficiency.
SUMMARY OF THE INVENTION
[0008] The present invention provides a catalyst for the
epoxidation of an olefin comprising a carrier and, deposited on the
carrier, silver, a rhenium promoter, a first co-promoter, and a
second co-promoter; wherein
the quantity of the rhenium promoter deposited on the carrier is
greater than 1 mmole/kg, relative to the weight of the catalyst;
the first co-promoter is selected from sulfur, phosphorus, boron,
and mixtures thereof; the second co-promoter is selected from
tungsten, molybdenum, chromium, and mixtures thereof; and the total
quantity of the first co-promoter and the second co-promoter
deposited on the carrier is at most 3.8 mmole/kg, relative to the
weight of the catalyst.
[0009] The invention also provides a process for preparing an
epoxidation catalyst comprising depositing silver, a rhenium
promoter, a first co-promoter, and a second co-promoter on a
carrier; wherein
the quantity of the rhenium promoter deposited on the carrier is
greater than 1 mmole/kg, relative to the weight of the catalyst;
the first co-promoter is selected from sulfur, phosphorus, boron,
and mixtures thereof; the second co-promoter is selected from
tungsten, molybdenum, chromium, and mixtures thereof; and the total
quantity of the first co-promoter and the second co-promoter
deposited on the carrier is at most 3.8 mmole/kg, relative to the
weight of the catalyst.
[0010] The invention also provides a process for the epoxidation of
an olefin comprising reacting the olefin with oxygen in the
presence of an epoxidation catalyst prepared according to this
invention.
[0011] Further, the invention provides a method of preparing a
1,2-diol, a 1,2-diol ether, a 1,2-carbonate, or an alkanolamine
comprising obtaining an olefin oxide by the process for the
epoxidation of an olefin according to this invention, and
converting the olefin oxide into the 1,2-diol, the 1,2-diol ether,
the 1,2-carbonate, or the alkanolamine.
BRIEF DESCRIPTION OF THE FIGURE
[0012] FIG. 1 shows the selectivity ("S mole-%") as a function of
the total quantity of first and second co-promoters ("mmole/kg"),
for the various catalysts of Series I, II, III, and IV, described
hereinafter.
DETAILED DESCRIPTION OF THE INVENTION
[0013] A highly selective epoxidation catalyst comprising a rhenium
promoter in a quantity of more than 1 mmole/kg of the catalyst and
a catalytically effective amount of silver as well as a first
co-promoter and a second co-promoter in a total quantity of at most
3.8 mmole/kg catalyst, in accordance with the invention, exhibits
an unexpected improvement in catalytic performance, in particular
an improvement in initial selectivity, compared to a like catalyst
not in accordance with the invention.
[0014] Generally, the epoxidation catalyst is a supported catalyst.
The carrier may be selected from a wide range of materials. Such
carrier materials may be natural or artificial inorganic materials
and they include silicon carbide, clays, pumice, zeolites,
charcoal, and alkaline earth metal carbonates, such as calcium
carbonate. Preferred are refractory carrier materials, such as
alumina, magnesia, zirconia, silica, and mixtures thereof. The most
preferred carrier material is .alpha.-alumina.
[0015] The surface area of the carrier may suitably be at least 0.1
m.sup.2/g, preferably at least 0.3 m.sup.2/g, more preferably at
least 0.5 m.sup.2/g, and in particular at least 0.6 m.sup.2/g,
relative to the weight of the carrier; and the surface area may
suitably be at most 20 m.sup.2/g, preferably at most 10 m.sup.2/g,
more preferably at most 6 m.sup.2/g, and in particular at most 4
m.sup.2/g, relative to the weight of the carrier. "Surface area" as
used herein is understood to relate to the surface area as
determined by the B.E.T. (Brunauer, Emmett and Teller) method as
described in Journal of the American Chemical Society 60 (1938) pp.
309-316. High surface area carriers, in particular when they are
alpha alumina carriers optionally comprising in addition silica,
alkali metal and/or alkaline earth metal components, provide
improved performance and stability of operation.
[0016] The water absorption of the carrier may suitably be at least
0.2 .mu.g, preferably at least 0.25 .mu.g, more preferably at least
0.3 .mu.g, most preferably at least 0.35 .mu.g; and the water
absorption may suitably be at most 0.85 .mu.g, preferably at most
0.7 .mu.g, more preferably at most 0.65 .mu.g, most preferably at
most 0.6 .mu.g. The water absorption of the carrier may be in the
range of from 0.2 to 0.85 .mu.g, preferably in the range of from
0.25 to 0.7 .mu.g, more preferably from 0.3 to 0.65 .mu.g, most
preferably from 0.3 to 0.6 .mu.g. A higher water absorption may be
in favor in view of a more efficient deposition of the metal and
promoters on the carrier by impregnation. However, at a higher
water absorption, the carrier, or the catalyst made therefrom, may
have lower crush strength. As used herein, water absorption is
deemed to have been measured in accordance with ASTM C20, and water
absorption is expressed as the weight of the water that can be
absorbed into the pores of the carrier, relative to the weight of
the carrier.
[0017] The carrier may be washed, to remove soluble residues,
before deposition of the catalyst ingredients on the carrier.
Additionally, the materials used to form the carrier, including the
burnout materials, may be washed to remove soluble residues. Such
carriers are described in U.S. Pat. No. 6,368,998 and
W0-A2-2007/095453, which are incorporated herein by reference. On
the other hand, unwashed carriers may also be used successfully.
Washing of the carrier generally occurs under conditions effective
to remove most of the soluble and/or ionizable materials from the
carrier.
[0018] The washing liquid may be, for example water, aqueous
solutions comprising one or more salts, or aqueous organic
diluents. Suitable salts for inclusion in an aqueous solution may
include, for example ammonium salts. Suitable ammonium salts may
include, for example ammonium nitrate, ammonium oxalate, ammonium
fluoride, and ammonium carboxylates, such as ammonium acetate,
ammonium citrate, ammonium hydrogencitrate, ammonium formate,
ammonium lactate, and ammonium tartrate. Suitable salts may also
include other types of nitrates such as alkali metal nitrates, for
example lithium nitrate, potassium nitrate and cesium nitrate.
Suitable quantities of total salt present in the aqueous solution
may be at least 0.001% w, in particular at least 0.005% w, more in
particular at least 0.01% w and at most 10% w, in particular at
most 1% w, for example 0.03% w. Suitable organic diluents which may
or may not be included are, for example, one or more of methanol,
ethanol, propanol, isopropanol, tetrahydrofuran, ethylene glycol,
ethylene glycol dimethyl ether, diethylene glycol dimethyl ether,
dimethylformamide, acetone or methyl ethyl ketone.
[0019] The preparation of the silver catalyst is known in the art
and the known methods are applicable to the preparation of the
catalyst which may be used in the practice of this invention.
Methods of depositing silver on the carrier include impregnating
the carrier or carrier bodies with a silver compound containing
cationic silver and/or complexed silver and performing a reduction
to form metallic silver particles. For further description of such
methods, reference may be made to U.S. Pat. No. 5,380,697, U.S.
Pat. No. 5,739,075, U.S. Pat. No. 4,766,105, and U.S. Pat. No.
6,368,998, which are incorporated herein by reference. Suitably,
silver dispersions, for example silver sols, may be used to deposit
silver on the carrier.
[0020] The reduction of cationic silver to metallic silver may be
accomplished during a step in which the catalyst is dried, so that
the reduction as such does not require a separate process step.
This may be the case if the silver containing impregnation solution
comprises a reducing agent, for example, an oxalate, a lactate or
formaldehyde.
[0021] Appreciable catalytic activity is obtained by employing a
silver content of the catalyst of at least 10 g/kg, relative to the
weight of the catalyst. Preferably, the catalyst comprises silver
in a quantity of from 10 to 500 g/kg, more preferably from 50 to
450 g/kg, for example 105 g/kg, or 120 g/kg, or 190 g/kg, or 250
g/kg, or 350 g/kg. As used herein, unless otherwise specified, the
weight of the catalyst is deemed to be the total weight of the
catalyst including the weight of the carrier and catalytic
components, for example silver, rhenium promoter, first and second
co-promoters and further elements, if any.
[0022] The catalyst for use in this invention additionally
comprises a rhenium promoter component deposited on the carrier in
a quantity of greater than 1 mmole/kg, relative to the weight of
the catalyst. Preferably, the rhenium promoter may be present in a
quantity of at least 1.25 mmole/kg, more preferably at least 1.5
mmole/kg, most preferably at least 2 mmole/kg of the catalyst.
Preferably, the rhenium promoter may be present in a quantity of at
most 500 mmole/kg, more preferably at most 50 mmole/kg, most
preferably at most 10 mmole/kg, relative to the weight of the
catalyst. Preferably, the rhenium promoter may be present in a
quantity in the range of from 1.25 to 50 mmole/kg, more preferably
from 1.75 to 25 mmole/kg, most preferably from 2 to 10 mmole/kg,
relative to the weight of the catalyst. The form in which the
rhenium promoter may be deposited onto the carrier is not material
to the invention. For example, the rhenium promoter may suitably be
provided as an oxide or as an oxyanion, for example, as a rhenate
or perrhenate, in salt or acid form.
[0023] The catalyst for use in this invention additionally
comprises a first co-promoter component. The first co-promoter may
be selected from sulfur, phosphorus, boron, and mixtures thereof.
It is particularly preferred that the first co-promoter comprises,
as an element, sulfur.
[0024] The catalyst for use in this invention additionally
comprises a second co-promoter component. The second co-promoter
component may be selected from tungsten, molybdenum, chromium, and
mixtures thereof. It is particularly preferred that the second
co-promoter component comprises, as an element, tungsten and/or
molybdenum, in particular tungsten. The form in which first
co-promoter and second co-promoter components may be deposited onto
the carrier is not material to the invention. For example, the
first co-promoter and second co-promoter components may suitably be
provided as an oxide or as an oxyanion, for example, as a
tungstate, molybdate, or sulfate, in salt or acid form.
[0025] The total quantity of the first co-promoter and the second
co-promoter deposited on the carrier is at most 3.8 mmole/kg,
calculated as the total quantity of the elements (i.e., the total
of sulfur, phosphorous, boron, tungsten, molybdenum and/or
chromium) relative to the weight of the catalyst. Preferably, the
total quantity of the first co-promoter and the second co-promoter
may be at most 3.5 mmole/kg, more preferably at most 3 mmole/kg of
catalyst. Preferably, the total quantity of the first co-promoter
and the second co-promoter may be at least 0.1 mmole/kg, more
preferably at least 0.5 mmole/kg, most preferably at least 1
mmole/kg of the catalyst.
[0026] In an embodiment, the molar ratio of the first co-promoter
to the second co-promoter may be greater than 1. In this
embodiment, the molar ratio of the first co-promoter to the second
co-promoter may preferably be at least 1.25, more preferably at
least 1.5, most preferably at least 2, in particular at least 2.5.
The molar ratio of the first co-promoter to the second co-promoter
may be at most 20, preferably at most 15, more preferably at most
10.
[0027] In an embodiment, the molar ratio of the rhenium promoter to
the second co-promoter may be greater than 1. In this embodiment,
the molar ratio of the rhenium promoter to the second co-promoter
may preferably be at least 1.25, more preferably at least 1.5. The
molar ratio of the rhenium promoter to the second co-promoter may
be at most 20, preferably at most 15, more preferably at most
10.
[0028] The catalyst may preferably also comprise a further element
deposited on the carrier. Eligible further elements may be selected
from nitrogen, fluorine, alkali metals, alkaline earth metals,
titanium, hafnium, zirconium, vanadium, thallium, thorium,
tantalum, niobium, gallium, germanium, and mixtures thereof.
Preferably, the alkali metals are selected from lithium, sodium,
rubidium and cesium. Most preferably, the alkali metal is lithium,
sodium and/or cesium. Preferably, the alkaline earth metals are
selected from calcium, magnesium and barium. Preferably, the
further element may be present in the catalyst in a total quantity
of from 0.01 to 500 mmole/kg, more preferably from 0.5 to 100
mmole/kg, the total quantity of the element relative to the weight
of the catalyst. The further element may be provided in any form.
For example, salts or hydroxides of an alkali metal or an alkaline
earth metal are suitable. For example, lithium compounds may be
lithium hydroxide or lithium nitrate.
[0029] In an embodiment, the catalyst may preferably further
comprise a potassium promoter deposited on the carrier. The
additional potassium promoter is preferred especially when the
carrier utilized in making the catalyst contains low levels of
leachable potassium. For example, the additional potassium promoter
is especially preferred when the carrier contains nitric acid
leachable potassium in a quantity of less than 85 ppmw, relative to
the weight of the carrier, suitably at most 80 ppmw, more suitably
at most 75 ppmw, most suitably at most 65 ppmw, same basis. The
additional potassium promoter is especially preferred when the
carrier contains water leachable potassium in a quantity of less
than 40 ppmw, relative to the weight of the carrier, suitably at
most 35 ppmw, more suitably at most 30 ppmw. In this embodiment,
the potassium promoter may be deposited in a quantity of at least
0.5 mmole/kg, preferably at least 1 mmole/kg, more preferably at
least 1.5 mmole/kg, most preferably at least 1.75 mmole/kg,
calculated as the total quantity of the potassium deposited
relative to the weight of the catalyst. The potassium promoter may
be deposited in a quantity of at most 20 mmole/kg, preferably at
most 15 mmole/kg, more preferably at most 10 mmole/kg, most
preferably at most 5 mmole/kg, on the same basis. The potassium
promoter may be deposited in a quantity in the range of from 0.5 to
20 mmole/kg, preferably from 1 to 15 mmole/kg, more preferably from
1.5 to 7.5 mmole/kg, most preferably from 1.75 to 5 mmole/kg, on
the same basis. A catalyst prepared in accordance with this
embodiment can exhibit an improvement in selectivity, activity,
and/or stability of the catalyst especially when operated under
conditions where the reaction feed contains low levels of carbon
dioxide, described hereinafter.
[0030] In an embodiment, the catalyst may preferably contain a
quantity of potassium such that the amount of water extractable
potassium of the catalyst may be at least 1.25 mmole/kg, relative
to the weight of the catalyst, suitably at least 1.5 mmole/kg, more
suitably at least 1.75 mmole/kg, same basis. Suitably, the catalyst
may contain water extractable potassium in a quantity of at most 10
mmole/kg, more suitably at most 7.5 mmole/kg, most suitably at most
5 mmole/kg, same basis. Suitably, the catalyst may contain water
extractable potassium in a quantity in the range of from 1.25 to 10
mmole/kg, more suitably from 1.5 to 7.5 mmole/kg, most suitably
from 1.75 to 5 mmole/kg, same basis. The source of water
extractable potassium may originate from the carrier and/or the
catalytic components. The quantity of water extractable potassium
in the catalyst is deemed to be the quantity insofar as it can be
extracted from the catalyst. The extraction involves extracting a
2-gram sample of the catalyst three times by heating it in 25-gram
portions of de-ionized water for 5 minutes at 100.degree. C. and
determining in the combined extracts the amount of potassium by
using a known method, for example atomic absorption
spectroscopy.
[0031] As used herein, unless otherwise specified, the quantity of
alkali metal present in the catalyst and the quantity of water
leachable components present in the carrier are deemed to be the
quantity insofar as it can be extracted from the catalyst or
carrier with de-ionized water at 100.degree. C. The extraction
method involves extracting a 10-gram sample of the catalyst or
carrier three times by heating it in 20 ml portions of de-ionized
water for 5 minutes at 100.degree. C. and determining in the
combined extracts the relevant metals by using a known method, for
example atomic absorption spectroscopy.
[0032] As used herein, unless otherwise specified, the quantity of
alkaline earth metal present in the catalyst and the quantity of
acid leachable components present in the carrier are deemed to be
the quantity insofar as it can be extracted from the catalyst or
carrier with 10% w nitric acid in de-ionized water at 100.degree.
C. The extraction method involves extracting a 10-gram sample of
the catalyst or carrier by boiling it with a 100 ml portion of 10%
w nitric acid for 30 minutes (1 atm., i.e. 101.3 kPa) and
determining in the combined extracts the relevant metals by using a
known method, for example atomic absorption spectroscopy. Reference
is made to U.S. Pat. No. 5,801,259, which is incorporated herein by
reference.
[0033] Although the present epoxidation process may be carried out
in many ways, it is preferred to carry it out as a gas phase
process, i.e. a process in which the feed is contacted in the gas
phase with the catalyst which is present as a solid material,
typically in a packed bed. Generally the process is carried out as
a continuous process.
[0034] The olefin for use in the present epoxidation process may be
any olefin, such as an aromatic olefin, for example styrene, or a
di-olefin, whether conjugated or not, for example 1,9-decadiene or
1,3-butadiene. Typically, the olefin is a monoolefin, for example
2-butene or isobutene. Preferably, the olefin is a
mono-.alpha.-olefin, for example 1-butene or propylene. The most
preferred olefin is ethylene. Suitably, mixtures of olefins may be
used.
[0035] The quantity of olefin present in the feed may be selected
within a wide range. Typically, the quantity of olefin present in
the feed will be at most 80 mole-%, relative to the total feed.
Preferably, it will be in the range of from 0.5 to 70 mole-%, in
particular from 1 to 60 mole-%, on the same basis. As used herein,
the feed is considered to be the composition which is contacted
with the catalyst.
[0036] The present epoxidation process may be air-based or
oxygen-based, see "Kirk-Othmer Encyclopedia of Chemical
Technology", 3.sup.rd edition, Volume 9, 1980, pp. 445-447. In the
air-based process, air or air enriched with oxygen is employed as
the source of the oxidizing agent while in the oxygen-based
processes high-purity (at least 95 mole-%) or very high purity (at
least 99.5 mole-%) oxygen is employed as the source of the
oxidizing agent. Reference may be made to U.S. Pat. No. 6,040,467,
incorporated by reference, for further description of oxygen-based
processes. Presently most epoxidation plants are oxygen-based and
this is a preferred embodiment of the present invention.
[0037] The quantity of oxygen present in the feed may be selected
within a wide range. However, in practice, oxygen is generally
applied in a quantity which avoids the flammable regime. Typically,
the quantity of oxygen applied will be within the range of from 1
to 15 mole-%, more typically from 2 to 12 mole-% of the total
feed.
[0038] In order to remain outside the flammable regime, the
quantity of oxygen present in the feed may be lowered as the
quantity of the olefin is increased. The actual safe operating
ranges depend, along with the feed composition, also on the
reaction conditions such as the reaction temperature and the
pressure.
[0039] A reaction modifier may be present in the feed for
increasing the selectively, suppressing the undesirable oxidation
of olefin or olefin oxide to carbon dioxide and water, relative to
the desired formation of olefin oxide. Many organic compounds,
especially organic halides and organic nitrogen compounds, may be
employed as the reaction modifiers. Nitrogen oxides, organic nitro
compounds such as nitromethane, nitroethane, and nitropropane,
hydrazine, hydroxylamine or ammonia may be employed as well. It is
frequently considered that under the operating conditions of olefin
epoxidation the nitrogen-containing reaction modifiers are
precursors of nitrates or nitrites, i.e. they are so-called
nitrate- or nitrite-forming compounds. Reference may be made to
EP-A-3642 and U.S. Pat. No. 4,822,900, which are incorporated
herein by reference, for further description of nitrogen-containing
reaction modifiers.
[0040] Organic halides are the preferred reaction modifiers, in
particular organic bromides, and more in particular organic
chlorides. Preferred organic halides are chlorohydrocarbons or
bromohydrocarbons. More preferably they are selected from the group
of methyl chloride, ethyl chloride, ethylene dichloride, ethylene
dibromide, vinyl chloride or a mixture thereof. Most preferred
reaction modifiers are ethyl chloride, vinyl chloride and ethylene
dichloride.
[0041] Suitable nitrogen oxides are of the general formula NO.sub.x
wherein x is in the range of from 1 to 2, and include for example
NO, N.sub.2O.sub.3 and N.sub.2O.sub.4. Suitable organic nitrogen
compounds are nitro compounds, nitroso compounds, amines, nitrates
and nitrites, for example nitromethane, 1-nitropropane or
2-nitropropane. In preferred embodiments, nitrate- or
nitrite-forming compounds, e.g. nitrogen oxides and/or organic
nitrogen compounds, are used together with an organic halide, in
particular an organic chloride.
[0042] The reaction modifiers are generally effective when used in
small quantities in the feed, for example up to 0.1 mole-%,
relative to the total feed, for example from 0.01.times.10.sup.-4
to 0.01 mole-%. In particular when the olefin is ethylene, it is
preferred that the reaction modifier is present in the feed in a
quantity of from 0.1.times.10.sup.-4 to 500.times.10.sup.-4 mole-%,
in particular from 0.2.times.10.sup.-4 to 200.times.10.sup.-4
mole-%, relative to the total feed.
[0043] In addition to the olefin, oxygen and the reaction modifier,
the feed may contain one or more optional components, such as
carbon dioxide, inert gases and saturated hydrocarbons. Carbon
dioxide is a by-product in the epoxidation process. However, carbon
dioxide generally has an adverse effect on the catalyst activity.
Typically, a quantity of carbon dioxide in the feed in excess of 25
mole-%, preferably in excess of 10 mole-%, relative to the total
feed, is avoided. A quantity of carbon dioxide of less than 3
mole-%, preferably less than 2 mole-%, in particular in the range
of from 0.3 to less than 1 mole-%, relative to the total feed, may
be employed. Under commercial operations, a quantity of carbon
dioxide of at least 0.1 mole-%, or at least 0.2 mole-%, relative to
the total feed, may be present in the feed. Inert gases, for
example nitrogen or argon, may be present in the feed in a quantity
of from 30 to 90 mole-%, typically from 40 to 80 mole-%. Suitable
saturated hydrocarbons are methane and ethane. If saturated
hydrocarbons are present, they may be present in a quantity of up
to 80 mole-%, relative to the total feed, in particular up to 75
mole-%. Frequently, they are present in a quantity of at least 30
mole-%, more frequently at least 40 mole-%. Saturated hydrocarbons
may be added to the feed in order to increase the oxygen
flammability limit.
[0044] The epoxidation process may be carried out using reaction
temperatures selected from a wide range. Preferably the reaction
temperature is in the range of from 150 to 325.degree. C., more
preferably in the range of from 180 to 300.degree. C.
[0045] The epoxidation process is preferably carried out at a
reactor inlet pressure in the range of from 1000 to 3500 kPa.
"GHSV" or Gas Hourly Space Velocity is the unit volume of gas at
normal temperature and pressure (0.degree. C., 1 atm, i.e. 101.3
kPa) passing over one unit volume of packed catalyst per hour.
Preferably, when the epoxidation process is a gas phase process
involving a packed catalyst bed, the GHSV is in the range of from
1500 to 10000 NI/(l.h). Preferably, the process is carried out at a
work rate in the range of from 0.5 to 10 kmole olefin oxide
produced per m.sup.3 of catalyst per hour, in particular 0.7 to 8
kmole olefin oxide produced per m.sup.3 of catalyst per hour, for
example kmole olefin oxide produced per m.sup.3 of catalyst per
hour. As used herein, the work rate is the amount of the olefin
oxide produced per unit volume of catalyst per hour and the
selectivity is the molar quantity of the olefin oxide formed
relative to the molar quantity of the olefin converted. Suitably,
the process is conducted under conditions where the olefin oxide
partial pressure in the product mix is in the range of from 5 to
200 kPa, for example 11 kPa, 27 kPa, 56 kPa, 77 kPa, 136 kPa, and
160 kPa. The term "product mix" as used herein is understood to
refer to the product recovered from the outlet of an epoxidation
reactor.
[0046] The olefin oxide produced may be recovered from the product
mix by using methods known in the art, for example by absorbing the
olefin oxide from a reactor outlet stream in water and optionally
recovering the olefin oxide from the aqueous solution by
distillation. At least a portion of the aqueous solution containing
the olefin oxide may be applied in a subsequent process for
converting the olefin oxide into a 1,2-diol, a 1,2-diol ether, a
1,2-carbonate, or an alkanolamine.
[0047] The olefin oxide produced in the epoxidation process may be
converted into a 1,2-diol, a 1,2-diol ether, a 1,2-carbonate, or an
alkanolamine. As this invention leads to a more attractive process
for the production of the olefin oxide, it concurrently leads to a
more attractive process which comprises producing the olefin oxide
in accordance with the invention and the subsequent use of the
obtained olefin oxide in the manufacture of the 1,2-diol, 1,2-diol
ether, 1,2-carbonate, and/or alkanolamine.
[0048] The conversion into the 1,2-diol or the 1,2-diol ether may
comprise, for example, reacting the olefin oxide with water,
suitably using an acidic or a basic catalyst. For example, for
making predominantly the 1,2-diol and less 1,2-diol ether, the
olefin oxide may be reacted with a ten fold molar excess of water,
in a liquid phase reaction in presence of an acid catalyst, e.g.
0.5-1.0% w sulfuric acid, based on the total reaction mixture, at
50-70.degree. C. at 1 bar absolute, or in a gas phase reaction at
130-240.degree. C. and 20-40 bar absolute, preferably in the
absence of a catalyst. The presence of such a large quantity of
water may favor the selective formation of 1,2-diol and may
function as a sink for the reaction exotherm, helping control the
reaction temperature. If the proportion of water is lowered, the
proportion of 1,2-diol ethers in the reaction mixture is increased.
The 1,2-diol ethers thus produced may be a di-ether, tri-ether,
tetra-ether or a subsequent ether. Alternative 1,2-diol ethers may
be prepared by converting the olefin oxide with an alcohol, in
particular a primary alcohol, such as methanol or ethanol, by
replacing at least a portion of the water by the alcohol.
[0049] The olefin oxide may be converted into the corresponding
1,2-carbonate by reacting the olefin oxide with carbon dioxide. If
desired, a 1,2-diol may be prepared by subsequently reacting the
1,2-carbonate with water or an alcohol to form the 1,2-diol. For
applicable methods, reference is made to U.S. Pat. No. 6,080,897,
which is incorporated herein by reference.
[0050] The conversion into the alkanolamine may comprise, for
example, reacting the olefin oxide with ammonia. Anhydrous ammonia
is typically used to favor the production of monoalkanolamine. For
methods applicable in the conversion of the olefin oxide into the
alkanolamine, reference may be made to, for example U.S. Pat. No.
4,845,296, which is incorporated herein by reference.
[0051] The 1,2-diol and the 1,2-diol ether may be used in a large
variety of industrial applications, for example in the fields of
food, beverages, tobacco, cosmetics, thermoplastic polymers,
curable resin systems, detergents, heat transfer systems, etc. The
1,2-carbonates may be used as a diluent, in particular as a
solvent. Alkanolamines may be used, for example, in the treating
("sweetening") of natural gas.
[0052] Unless specified otherwise, the low-molecular weight organic
compounds mentioned herein, for example the olefins, 1,2-diols,
1,2-diol ethers, 1,2-carbonates, alkanolamines, and reaction
modifiers, have typically at most 40 carbon atoms, more typically
at most 20 carbon atoms, in particular at most 10 carbon atoms,
more in particular at most 6 carbon atoms. As defined herein,
ranges for numbers of carbon atoms (i.e. carbon number) include the
numbers specified for the limits of the ranges.
[0053] Having generally described the invention, a further
understanding may be obtained by reference to the following
examples, which are provided for purposes of illustration only and
are not intended to be limiting unless otherwise specified.
EXAMPLES
Example 1
Preparation of Stock Silver Solution
[0054] This example describes the preparation of a stock silver
impregnation solution used in preparing Catalyst A in Example
2.
[0055] A silver-amine-oxalate stock solution was prepared by the
following procedure:
[0056] In a 5-liter stainless steel beaker, 415 g of reagent-grade
sodium hydroxide were dissolved in 2340 ml de-ionized water, and
the temperature was adjusted to 50.degree. C.
[0057] In a 4-liter stainless steel beaker, 1699 g high purity
"Spectropure" silver nitrate was dissolved in 2100 ml de-ionized
water, and the temperature was adjusted to 50.degree. C.
[0058] The sodium hydroxide solution was added slowly to the silver
nitrate solution, with stirring, while maintaining a solution
temperature of 50.degree. C. This mixture was stirred for 15
minutes. The pH of the solution was maintained at above 10 by the
addition of sodium hydroxide solution as required.
[0059] Water was removed from the precipitate created in the mixing
step and the conductivity of the water, which contained sodium and
nitrate ions, was measured. An amount of fresh deionized water
equal to the amount removed was added back to the silver solution.
The solution was stirred for 15 minutes at 40.degree. C. The
process was repeated until the conductivity of the water removed
was less than 90 .mu.mho/cm. 1500 ml fresh deionized water was then
added. 630 g of high-purity oxalic acid dihydrate were added in
approximately 100 g increments. The temperature was kept at
40.degree. C. (.+-.5.degree. C.) and the pH of the solution was
monitored during the addition of the last 130 grams of oxalic acid
dihydrate to ensure that the pH did not drop below 7.8 for an
extended period of time.
[0060] Water was removed from this mixture to leave a highly
concentrated silver-containing slurry. The silver oxalate slurry
was cooled to 30.degree. C.
[0061] 699 g of 92 weight percent ethylenediamine (8% de-ionized
water) was added while maintaining a temperature no greater than
30.degree. C. The final solution was used as a stock silver
impregnation solution for preparing Catalyst A.
Example 2
Preparation of Catalysts
Catalyst A:
[0062] Catalyst A was prepared by the following procedure: To 404
grams of stock silver solution of specific gravity 1.545 g/ml was
added 0.3630 g of ammonium perrhenate in 2 g of 1:1
ethylenediamine/water; 0.1012 g of ammonium metatungstate dissolved
in 2 g of 1:1 ammonia/water; 0.1732 g of lithium sulfate
monohydrate dissolved in 2 g of water; and 0.4259 g of lithium
hydroxide monohydrate dissolved in water. Additional water was
added to adjust the specific gravity of the solution to 1.528 g/ml.
100 g of the resulting solution was mixed with 0.2727 g of 50% w
cesium hydroxide solution, producing the final impregnation
solution. A vessel containing 30 grams of Carrier A hollow
cylinders, see Table I below, was evacuated to 20 mm Hg for 1
minute and the final impregnation solution was added to Carrier A
while under vacuum, then the vacuum was released and the carrier
allowed to contact the liquid for 3 minutes. The impregnated
Carrier A was then centrifuged at 500 rpm for 2 minutes to remove
excess liquid. Impregnated Carrier A was placed in a vibrating
shaker and dried in air flowing at a rate of 16.2 Nl/h at
250.degree. C. for 7 minutes producing Catalyst A.
[0063] The final composition of Catalyst A comprised the following,
calculated on the basis of pore volume impregnation: 17.2% w
silver; 2 mmole Re/kg; 0.6 mmole W/kg; 2 mmole S/kg; 19 mmole
Li/kg; and 5.6 mmole Cs/kg. These values are relative to the weight
of the catalyst.
TABLE-US-00001 TABLE I Carrier A Properties Surface Area
(m.sup.2/g) 0.75 Water Absorption (%) 47.2 Packing Density
(kg/m.sup.3) 838 alpha alumina content (%) 98.4 Nitric Acid
Leachables: Na 116 K 87 Ca 567 Al 607 Mg 81 SiO.sub.2 1474
Catalyst B:
[0064] Catalyst B was prepared in a similar manner as Catalyst A.
The final composition of Catalyst B comprised the following,
calculated on the basis of pore volume impregnation: 17.2% w
silver; 2 mmole Re/kg; 0.6 mmole W/kg; 3 mmole S/kg; 21 mmole
Li/kg; and 6.4 mmole Cs/kg. These values are relative to the weight
of the catalyst.
Catalyst C:
[0065] Catalyst C was prepared in a similar manner as Catalyst A.
The final composition of Catalyst C comprised the following,
calculated on the basis of pore volume impregnation: 17.5% w
silver; 2 mmole Re/kg; 1 mmole W/kg; 1 mmole S/kg; 17 mmole Li/kg;
and 4.9 mmole Cs/kg. These values are relative to the weight of the
catalyst.
Catalyst D:
[0066] Catalyst D was prepared in a similar manner as Catalyst A,
using 30 grams of Carrier A. To 198.4 grams of stock silver
solution of specific gravity 1.551 g/ml was added 0.1833 g of
ammonium perrhenate in 2 g of 1:1 ethylenediamine/water; 0.0362 g
of ammonium molybdate dissolved in 2 g of 50:50 ammonium
hydroxide/water; 0.1312 g of lithium sulfate monohydrate dissolved
in 2 g of water; and 0.2151 g of lithium hydroxide monohydrate
dissolved in water. Additional water was added to adjust the
specific gravity of the solution to 1.528 g/ml. 50 g of the
resulting solution was mixed with 0.1591 g of 50% w cesium
hydroxide solution, producing the impregnation solution. This final
impregnation solution was used to prepare Catalyst D.
[0067] The final composition of Catalyst D comprised the following,
calculated on the basis of pore volume impregnation: 17.2% w
silver; 2 mmole Re/kg; 0.6 mmole Mo/kg; 3 mmole S/kg; 21 mmole
Li/kg; and 6.4 mmole Cs/kg. These values are relative to the weight
of the catalyst.
Catalyst E:
[0068] Catalyst E was prepared in a similar manner as Catalyst D.
The final composition of Catalyst E comprised the following,
calculated on the basis of pore volume impregnation: 17.2% w
silver; 2 mmole Re/kg; 0.6 mmole Mo/kg; 2 mmole S/kg; 19 mmole
Li/kg; and 6 mmole Cs/kg. These values are relative to the weight
of the catalyst.
Catalyst F (Comparative):
[0069] Catalyst F was prepared in a similar manner as Catalyst A.
The final composition of Catalyst F comprised the following,
calculated on the basis of pore volume impregnation: 17.2% w
silver; 2 mmole Re/kg; 2 mmole W/kg; 2 mmole S/kg; 19 mmole Li/kg;
and 5.6 mmole Cs/kg. These values are relative to the weight of the
catalyst.
Catalyst G (Comparative):
[0070] Catalyst G was prepared in a similar manner as Catalyst A.
The final composition of Catalyst G comprised the following,
calculated on the basis of pore volume impregnation: 17.5% w
silver; 1 mmole Re/kg; 1 mmole W/kg; 1 mmole S/kg; 17 mmole Li/kg;
and 4.5 mmole Cs/kg. These values are relative to the weight of the
catalyst.
Catalyst H (Comparative):
[0071] Catalyst H was prepared in a similar manner as Catalyst A.
The final composition of Catalyst H comprised the following,
calculated on the basis of pore volume impregnation: 17.5% w
silver; 1 mmole Re/kg; 2 mmole W/kg; 2 mmole S/kg; 19 mmole Li/kg;
and 4.1 mmole Cs/kg. These values are relative to the weight of the
catalyst.
Catalyst I (Comparative):
[0072] Catalyst I was prepared in a similar manner as Catalyst A.
The final composition of Catalyst I comprised the following,
calculated on the basis of pore volume impregnation: 17.5% w
silver; 1 mmole Re/kg; 0.6 mmole W/kg; 2 mmole S/kg; 19 mmole
Li/kg; and 4.5 mmole Cs/kg. These values are relative to the weight
of the catalyst.
Catalyst J (Comparative):
[0073] Catalyst J was prepared in a similar manner as Catalyst A.
The final composition of Catalyst J comprised the following,
calculated on the basis of pore volume impregnation: 17.2% w
silver; 2 mmole Re/kg; 0.6 mmole W/kg; 15 mmole Li/kg; and 5.6
mmole Cs/kg. These values are relative to the weight of the
catalyst.
Catalyst K (Comparative):
[0074] Catalyst K was prepared in a similar manner as Catalyst A.
The final composition of Catalyst K comprised the following,
calculated on the basis of pore volume impregnation: 17.2% w
silver; 2 mmole Re/kg; 2 mmole W/kg; 15 mmole Li/kg; and 4.1 mmole
Cs/kg. These values are relative to the weight of the catalyst.
Catalyst L (Comparative):
[0075] Catalyst L was prepared in a similar manner as Catalyst A.
The final composition of Catalyst L comprised the following,
calculated on the basis of pore volume impregnation: 17.2% w
silver; 2 mmole Re/kg; 3 mmole S/kg; 21 mmole Li/kg; and 6.8 mmole
Cs/kg. These values are relative to the weight of the catalyst.
Catalyst M (Comparative):
[0076] Catalyst M was prepared in a similar manner as Catalyst A.
The final composition of Catalyst M comprised the following,
calculated on the basis of pore volume impregnation: 17.2% w
silver; 2 mmole Re/kg; 2 mmole S/kg; 19 mmole Li/kg; and 5.6 mmole
Cs/kg. These values are relative to the weight of the catalyst.
[0077] The cesium amounts of the above catalysts are the optimized
cesium amounts with respect to the initial selectivity performance
of the catalysts.
Example 3
Testing of Catalysts
[0078] The catalysts were used to produce ethylene oxide from
ethylene and oxygen. To do this, 3 to 5 g of the crushed catalyst
samples were loaded into separate stainless steel U-shaped tubes.
Each tube was immersed in a molten metal bath (heat medium) and the
ends were connected to a gas flow system. The weight of catalyst
used and the inlet gas flow rate were adjusted to give a gas hourly
space velocity of 3300 Nl/(l.h), as calculated for uncrushed
catalyst. The inlet gas pressure was 1550 kPa (absolute).
[0079] The gas mixture passed through the catalyst bed, in a
"once-through" operation, during the entire test run, consisted of
30.0 volume percent ethylene, 8.0 volume percent oxygen, 5.0 volume
percent carbon dioxide, 57 volume percent nitrogen and 0 to 4.0
parts per million by volume (ppmv) ethyl chloride.
[0080] Prior to startup, the catalysts were pre-treated for 3 hours
with a gas mixture of 11.4 mole-% oxygen, 7 mole-% carbon dioxide
and 81.6 mole-% nitrogen at 280.degree. C., except Catalysts A, B,
J, and M which were pre-treated for 3 hours under a flow of
nitrogen at 225.degree. C. Then the reactor was either cooled down
or heated to 240.degree. C. and testing gas mixture was introduced.
The temperature was then adjusted so as to achieve a constant
ethylene oxide content of 3.09 volume percent in the outlet gas
stream. The quantity of ethyl chloride was varied to obtain maximum
selectivity. Catalysts B, E and L were additionally subjected to
conditions where the ethyl chloride was decreased to zero for 4 to
24 hours during which time the temperature was changed to
250-260.degree. C. Initial performance data at this conversion
level was measured between 1 to 7 days of operation. The
performance data is summarized below in Table II. Selectivity and
temperature values corresponding to increasing cumulative ethylene
oxide production would also be measured in order to obtain catalyst
stability data.
[0081] As observed from the data in Table II, Catalysts A, B, C, D,
and E, having a total quantity of first and second co-promoters of
at most 3.8 mmole/kg catalyst, exhibit an unexpected improvement in
initial selectivity at the same ethylene oxide production levels,
relative to Catalyst F which has a total quantity of first and
second co-promoters of 4 mmole/kg catalyst. This technical effect
is shown in FIG. 1. FIG. 1 is a graph showing the selectivity (S
mole-%) relative to the total quantity of co-promoter(s)
(mmole/kg).
[0082] Series II relates to Catalysts A, B, C, and F which contain
2 mmole of rhenium per kilogram of catalyst, sulfur as the first
co-promoter, and tungsten as the second co-promoter. Series III
relates to Catalysts D and E which contain 2 mmole of rhenium per
kilogram of catalyst; sulfur as the first co-promoter; molybdenum
as the second co-promoter.
[0083] Series I relates to Catalysts G, H and I which contain 1
mmole of rhenium per kilogram of catalyst, sulfur as the first
co-promoter, and tungsten as the second co-promoter. The advantage
in initial selectivity was not observed for the catalysts of Series
I.
[0084] Series IV relates to Catalysts J, K, L, and M which contain
2 mmole of rhenium per kilogram of catalyst and either a first
co-promoter of sulfur or a second co-promoter of tungsten.
TABLE-US-00002 TABLE II Total Cs Ag Co- Selectivity Temperature
(mmole/ Content Re W Mo S Promoters Initial Initial Catalyst Series
kg) % w (mmole/kg) (mmole/kg) (mmole/kg) (mmole/kg) (mmole/kg) (%)
(.degree. C.) A *) II 5.6 17.2 2 0.6 -- 2 2.6 89.8 250 B *) II 6.4
17.2 2 0.6 -- 3 3.6 89.6 251 C *) II 4.9 17.5 2 1 -- 1 2 90.3 262 D
*) III 6.4 17.2 2 -- 0.6 3 3.6 90.7 261 E *) III 6.0 17.2 2 -- 0.6
2 2.6 89.5 261 F **) II 5.6 17.2 2 2 -- 2 4 89.2 268 G **) I 4.5
17.5 1 1 -- 1 2 86.9 265 H **) I 4.1 17.5 1 2 -- 2 4 87.9 264 I **)
I 4.5 17.5 1 0.6 -- 2 2.6 87.5 256 J **) IV 5.6 17.2 2 0.6 -- --
0.6 87.2 252 K **) IV 4.1 17.2 2 2 -- -- 2 89.3 261 L **) IV 6.8
17.2 2 -- -- 3 3 88.3 251 M **) IV 5.6 17.2 2 -- -- 2 2 86.8 239 *)
according to the invention **) comparative
Example 4
[0085] Catalyst N was prepared using Carrier B and having a final
composition of the following, calculated on the basis of pore
volume impregnation: 17.5% w silver; 2 mmole Re/kg; 0.6 mmole W/kg;
2 mmole S/kg; 19 mmole Li/kg; 2 mmole K/kg; and 3.8 mmole Cs/kg.
These values are relative to the weight of the catalyst. Ammonium
perrhenate, ammonium metatungstate, ammonium sulfate, lithium
hydroxide, potassium nitrate and cesium hydroxide were used to
prepare Catalyst N.
TABLE-US-00003 TABLE III Carrier B Properties Surface Area
(m.sup.2/g) 0.73 Water Absorption (%) 47.8 Packing Density
(kg/m.sup.3) 838 alpha alumina content (%) 98.4 Nitric Acid
Leachable, ppmw: Na 131 K 83 Ca 533 Al 655 Mg 74 SiO.sub.2 1456
[0086] A tubular pilot reactor was charged with 12.24 kg of whole
catalyst pellets in the form of a hollow cylinder having a nominal
outer diameter of 8 mm, a nominal inner diameter of 1 mm and a
nominal length of 8 mm. The coolant (water) surrounding the tubular
reactor was heated from 40 to 220.degree. C. over 17 hours and a
flow of N.sub.2 gas at GHSV of 1100 Nl/l/h was introduced into the
reactor tube. Once the coolant temperature reached 220.degree. C.,
ethylene was added to the reactor feed gas and brought to 25 vol %.
After the desired ethylene concentration was achieved, air was
introduced in the reactor feed to initiate reaction of ethylene and
oxygen to ethylene oxide. At essentially the same time as air was
introduced to the reactor, ethyl chloride was introduced and
brought to a concentration of 2-2.5 ppmv. During the next 6 hours
of operation, the air feed rate was increased until an oxygen
concentration of 4.0 vol % was achieved at the reactor inlet. As
the oxygen was increased, the coolant temperature was increased to
235.degree. C., carbon dioxide was introduced and brought to 0.8
vol %, and the total flow was increased to a GHSV of 3320 Nl/l/h.
The inlet pressure to the reactor was maintained at 241 psig
throughout the experiment. A total of 0.15 grams of ethyl chloride
per kilogram of catalyst was introduced. For the next 17 hours,
ethyl chloride was reduced to 1.4 ppmv and all other conditions
were held constant at GHSV of 3320 Nl/l/h, 235.degree. C. coolant
temperature, 241 psig inlet pressure, and ethylene/oxygen/carbon
dioxide composition of 25:4:0.8. During the next 7 hours, ethylene
was increased from 25 to 35 vol %, oxygen was increased from 4.0 to
7.5 vol %, and ethyl chloride was increased from 1.4 ppmv to 1.91
ppmv. All other gas flows and compositions were held constant. At
the end of this step, the coolant temperature was adjusted to
227.degree. C. to achieve an ethylene oxide concentration of 2.7
vol % in the outlet of the reactor. During the following 24 hours,
the ethyl chloride concentration was increased to 2.05 ppmv to
obtain the optimal catalyst selectivity. At the end of the start-up
process (i.e., during step 6), the selectivity was 90.3% at a
temperature of 228.degree. C. Details of the changing reactor
conditions are set out in Table IV.
TABLE-US-00004 TABLE IV Temperature, GHSV, Ethyl Chloride, Step
.degree. C. Nl/l/h O.sub.2, % C.sub.2H.sub.4, % CO.sub.2, % ppmv
Time, h 1 40 to 220 1100 0 0 0 0 17 2 220 1100 0 25 0 0 1 3 220 to
235 1100 to 3320 0 to 4 25 0-0.8 2 to 2.5 6 4 235 3320 4 25 0.8 1.4
17 5 235 to 227 3320 4 to 7.5 25 to 35 0.8 1.4 to 1.91 7 6 228 3320
7.5 35 0.8 2.05 24
During the start-up process and initial epoxidation production, the
quantity of ethylene may be maintained at a constant level and
different amounts may be utilized, for example the quantity of
ethylene may be 25 mole-%, 35 mole-%, or 40 mole-%. The quantity of
oxygen may be varied within flammability limits. The length of step
4 may be varied from 1 to 30 hours, shorter periods of time may be
preferred for higher production levels.
* * * * *